This invention relates generally to shaft couplings and more specifically to shaft couplings involving tubular shafts which are squeezed by a pinch bolt.
Tubular shafts are often used to transfer torque from one location to another since they can transfer a given torque at a lesser weight than a solid shaft can. Tubular shafts are used often in devices such as steering column assemblies to transfer torque where the tubular shafts are attached to another member, such as another shaft or the housing of a universal joint. A shaft coupling is commonly used for this purpose.
A known shaft coupling comprises a tubular shaft and a housing for a universal joint, both designed to transfer torque. The housing of the universal joint has a collar and the tubular shaft and the collar are attached by a pinch bolt. The tubular shaft includes an end portion which has flat parallel segments opposite each other. The flat parallel segments have aligned bolt holes so that a shank of the pinch bolt may pass through.
The collar for the housing for the universal joint fits over the end portion of the tubular shaft. The collar has flat parallel segments abutting the flat parallel segments of the end portion of the tubular shaft so that torque may be transmitted between the tubular shaft and the collar. The flat parallel segments of the member have bolt holes which are aligned with the bolt holes of the tubular shaft so that the shank of the pinch bolt may pass through the collar and the tubular shaft at the same time. In operation, the end portion of the tubular shaft is fitted inside the collar of the housing, and is attached to the collar by the pinch bolt.
A very tight connection is desired so that the coupling does not become loose after extended periods of operation. Consequently the pinch bolt is torqued down as much as possible in order to extend the useful service life of the shaft coupling. However, there is a practical limit in the prior art shaft coupling because even though the tubular shaft transfers torque well, it does not hold up as well as a solid shaft under the radial forces produced by the pinch bolt. Moreover, if the pinch bolt is torqued down too tight, elastic deformation may occur in the tubular shaft, lowering the area of contact with the collar which shortens the service life and reduces the torque capacity of the shaft coupling. Thus, there is a need to strengthen the tubular shaft so that a larger radial force may be applied and a longer service life and higher torque capacity for the shaft coupling may be achieved.